Size dependence of the pressure-induced γ to α structural phase transition in iron oxide nanocrystals

S. M. Clark*, S. G. Prilliman, C. K. Erdonmez, A. P. Alivisatos

*Corresponding author for this work

Research output: Contribution to journalArticle

44 Citations (Scopus)

Abstract

The size trend for the pressure-induced γ-Fe2O3 (maghemite) to α-Fe2O3 (haematite) structural phase transition in nanocrystals has been observed. The transition pressure was found to increase with decreasing nanocrystal size: 7 nm nanocrystals transformed at 27 ± 2 GPa, 5 nm ones at 34 ± 3 GPa and 3 nm ones at 37 ± 2 GPa. Annealing of a bulk sample of γ-Fe2O3 was found to reduce the transition pressure from 35 ± 2 to 24 ± 2 GPa. The bulk modulus was determined as 262 ± 6 GPa for 7 nm nanocrystals of γ-Fe2O3, which is significantly higher than the value of 190 ± 6 GPa that we measured for bulk samples. For α-Fe2O3, the bulk moduli for 7 nm nanocrystals (336 ± 5) and the bulk (300 ± 30) were found to be almost the same within error. The bulk modulus for the γ phase was found to decrease with decreasing particle size between 10 and 3.2 nm particle size. Values for the ambient pressure molar volume were found within 1% to be: 33.0 cm3 mol-1 for bulk γ-Fe2O3; 32.8 cm 3 mol-1 for 7 nm diameter γ-Fe2O 3 nanocrystals; 30.7 cm3 mol-1 for bulk α-Fe2O3; and 30.6 cm3 mol-1 for α-Fe2O3 nanocrystals.

Original languageEnglish
Pages (from-to)2813-2818
Number of pages6
JournalNanotechnology
Volume16
Issue number12
DOIs
Publication statusPublished - 1 Dec 2005
Externally publishedYes

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